Various natural occurring clays may be blended with various elastomers which usually act as relatively inactive fillers in rubber compositions insofar as reinforcement of the rubber compositions is concerned. Representative of such clays are, in general, for example, bentonite and kaolin clays. Such clays are conventionally hydrophilic in nature and therefore are relatively incompatible with diene-based elastomers.
However, some clays, such as, for example, smectite clays, and particularly montmorillonite clays which might be considered to be in a nature of a species of a bentonite clay, can be changed from being hydrophilic in nature to a clay being hydrophobic in nature and therefore more compatible with diene-based elastomers.
From an historical perspective, some naturally occurring layered clay minerals such as, for example, montmorillonite clay, which are hydrophilic in nature, are composed of a plurality of platelets which have a tendency to swell in the presence of water as a result of an associated increase of the distance between the platelets.
Such clay, particularly a montmorillonite clay, may be intercalated by chemical ion exchange methods. For such intercalation of a montmorillonite clay, the clay may be immersed in water to cause the clay to swell and a quaternary ammonium salt introduced, or included, in the water to cause the typically occurring sodium ions in the space between the platelets to be exchanged with the quaternary ammonium ion from the quaternary ammonium salt to further expand the distance between the platelets and to thereby intercalate the clay. If an alkyl quaternary ammonium salt is used which can impart aliphatic hydrocarbon chains on the surface of the clay by the ion exchange process, the intercalated clay can become more hydrophobic in nature and therefore more compatible with elastomers, particularly with diene-based elastomers.
The intercalated clay may then be dried and blended with an elastomer(s) under conditions of elevated temperature and relatively high shear conditions to cause the swelled and intercalated clay to at least partially exfoliate, or separate into small, individual platelets within the rubber composition and to contribute to the reinforcement of the rubber composition itself. Such intercalation procedure for montmorillonite clay and use thereof for reinforcement of rubber compositions is well known to those having skill in such art.
For example, an intercalated clay might be historically prepared by obtaining a smectite clay, other than a kaolin type clay, namely a clay such as, for example, a montmorillonite clay, which is comprised of a plurality of stacked layers, or platelets and which is swellable upon dispersion in water; dispersing the clay in an aqueous solution of a surfactant (e.g. a quaternary ammonium salt) which causes the clay to swell so that the average spacing between the platelets typically expands from about 4 Angstroms to an average spacing in a range of about 10 to about 30 Angstroms; followed by drying the treated, or intercalated, clay.
The smectite clay (e.g. montmorillonite clay) for use in this invention contains sodium ions between its layered platelets and the larger surfactant molecules contained in the water solution in which the clay is immersed position themselves between the layered platelets by an ion exchange with the sodium ions to cause or otherwise enhance the separation of the platelets to make the platelets more amenable to subsequent exfoliation.
Hydrophilic clays typically have a relatively high concentration of oxygen on their exposed surfaces and are therefore relatively incompatible with diene-based elastomers.
It is therefore often desirable to create intercalated clays which are more hydrophobic in nature by forming a predominance of aliphatic hydrocarbon chains on its exposed surfaces, thereby causing the intercalated clay to be more hydrophobic in nature. Such converted intercalated clays having aliphatic hydrocarbon chains on their surface are sometimes referred to as organoclays or might be sometimes as organophillic clays.
As hereinbefore related, the formation of aliphatic hydrocarbon chains on the surfaces of intercalated clay, and associated exfoliated platelets thereof may be accomplished, for example, by utilization of alkyl quaternary ammonium salts for treatment of the clay in its aqueous dispersion to create organoclays which are hydrophobic in nature which are more compatible with diene-based elastomers and therefore more readily dispersible in such elastomeric compositions.
Such conversion of naturally occurring hydrophilic clays such as montmorillonite clay to more hydrophobic organoclays for a more suitable dispersion in various elastomers is well known to those having skill in such art.
However, such operational steps to create more useful organoclays of a hydrophobic nature, including associated intercalated clays and exfoliated clay platelets for reinforcement of rubber composition, are process intensive. This is because of the aforesaid considerable and involved sequential steps of, for example, first immersing the hydrophilic clay in water which contains, for example, a suitable quaternary ammonium salt to cause it to swell and intercalate with an associated conversion of the clay to a hydrophobic organoclay, drying the organoclay, followed by dispersing the intercalated organoclay within an elastomer under high sheer mixing conditions to cause the intercalated organoclay to at least partially exfoliate into a plurality of individual platelets.
Accordingly, it is desired to enhance a creation of an intercalated and exfoliated montmorillonite clay which is hydrophobic in nature for use in the reinforcement of rubber compositions.
Historically, blending of an organoclay with a thermoplastic or thermosetting polymer by a melt blending process is discussed in U.S. Pat. Nos. 4,739,007; 4,810,734; 5,385,776; 5,578,672 and 5,840,796. Historically, blending of an adduct of a mineral filler such as for example a montmorillonite clay, and a quaternary ammonium salt with at least one rubber and an organosilane is discussed in U.S. Pat. No. 4,431,755.
For the description of this invention, the term “elastomer exfoliated nanoclay composite” means, unless otherwise indicated herein, an elastomer composition which contains an intercalated clay, in which the intercalated clay is at least partially exfoliated in situ within the elastomer host, particularly a smectite clay as a sodium montmorillonite clay, in which the particles are primarily organoclay platelets, and fragments of such platelets, wherein the platelets are somewhat circular and possibly elliptical in shape having an average, somewhat irregular, length and width, in a range of, for example, about 100 to about 1000 nanometers.
The smectite clay, preferably the montmorillonite clay, for use in this invention, might be described, for example, as a naturally occurring clay of a structure which is composed of a plurality of stacked, thin and relatively flat, layers, where such individual layers may be of a structure viewed as being composed of very thin octahedral shaped alumina layer sandwiched between two very thin tetrahedrally shaped silica layers to form an aluminosilicate structure. Generally, for such aluminosilicate structure in the naturally occurring montmorillonite clay, some of the aluminum cations (Al+3) are viewed as having been replaced by magnesium cations (Mg+2) which results in a net negative charge to the platelet layers of the clay structure. Such negative charge is viewed as being balanced in the naturally occurring clay with hydrated sodium, lithium, magnesium, calcium and/or potassium cations within the spacing (sometimes referred to as “galleries”) between the aforesaid aluminosilicate layers, or platelets. The average spacing, between the layers, or platelets, typically in a range of about 1 to about 5 Angstroms, is largely determined by the nature of such aforesaid cation residues contained with the spacing and by the degree of hydration and which may be measured by x-ray diffraction method.
In the description of this invention, the term “phr” is used to designate parts by weight of a material per 100 parts by weight of elastomer. The terms “rubber” and “elastomer” may be used interchangeably unless otherwise indicated. The terms “vulcanized” and “cured” may be used interchangeably, as well as “unvulcanized” or “uncured”, unless otherwise indicated.